Integrins and other receptors for extracellular matrix proteins such as fibronectin, collagen, and laminin are thought to play important roles in embryonic development and metastasis. Monoclonal antibodies against specific integrins and recombinant DNA approaches are being applied to understand their mechanisms of function, as well as the developmental or potential medical sequelae of inhibiting such receptors. Inhibition of certain beta1 integrin receptors blocked migration of a variety of cell types in vitro and disrupted normal embryonic development. Migration of human keratinocytes and several tumor lines on fibronectin depended on normal function of the mature form of the integrin alpah5 beta1, whereas migration of various cells in collagen was dependent on alpha2 beta1. Rates of cell migration depended on the avidity of receptor-substrate interactions. The essential function of such receptors in tumor cell migration and invasion was demonstrated in vitro and is being tested in vivo. A non-integrin 47 kD protein that also binds to collagen and is decreased in malignant cells was sequenced at the cDNA level and shown to be a member of the serpin family. Regulation of the localization and functional association of matrix receptors with the cytoskeleton is currently being explored using novel intermolecular chimeras.